In Alastair Campbell's introduction to the second volume of his unexpurgated diaries (volumes three and four are to follow shortly, at which point, he says, he will have provided the world with "the longest, and possibly the most complete, single account of life at the heart of the Blair team"), the former New Labour spin doctor professes himself still to be amazed at what the Labour government achieved during its first two years in power: independence for the Bank of England, the minimum wage, devolution to Scotland and Wales and a peace agreement in Northern Ireland.

And it's true that Power and the People touches on all these things, eventually. The effect on the reader, however, is not so much one of astonishment as exhaustion. Rarely have I put down a book with such a feeling of relief, even of escape. For its tone could not be less celebratory if it tried. The New Labour government's achievements, such as they are, are buried beneath a vast, verbal slagheap of bitchiness, rows and moaning, the only light relief provided by the antics of two men: Robin Cook and Michael (now Lord) Levy. The former foreign secretary, we learn, believed the nation just could not live without seeing photographs of his wedding to his diary secretary, Gaynor Regan; according to Campbell, pretty much the only thing standing between Cook and a deal with Hello! was him.

Michael Levy, meanwhile, comes off as New Labour's very own Wally (as in Where's Wally?). Campbell is always telling him that he must not be caught on camera with Blair. But he can't help himself! The combined allure of the prime minister and the flashbulbs of the world's media is quite simply impossible to resist.

Much of the tone of the book is simply a function of Campbell's depressive personality. Within weeks of Blair's arrival at Downing Street, he is complaining of exhaustion; there are mornings, he writes, when he finds it hard to get out of bed. But there are other things at play, too. The flipside of Campbell's fragility is a giant ego; his self-doubt is always sheathed in protective layers of self-regard. By his account, no one in the government is any good. Gordon Brown is "impossible" (Campbell now finally admits that he was the source of Andrew Rawnsley's story about Brown's "psychological flaws"). Peter Mandelson is vain, pompous and always having hissy fits. Ditto Robin Cook. Harriet Harman is not up to her job at social security and Frank Field, her junior minister, is a "creepy" waffler who cannot deliver. Mo Mowlam is clumsy and contradictory. Clare Short should be sacked. Frank Dobson has "no drive". Donald Dewar is "sad".

The only person he has any time for at all is John Prescott, whose loyalty means that he is at least biddable, even if he does muddle his acronyms. Needless to say, Campbell, by contrast, is utterly brilliant. "I was always struck at these meetings how much ministers looked to me for the ideas and the execution," he writes, following a gathering to discuss progress on Saddam and his – ha! – weapons of mass destruction.

Later on, during the Kosovo crisis, Campbell feels the need to have a word with Jamie Shea, Nato's spokesman, about the alliance's media operation. Is Shea put out by this? He is not. "He was very receptive, said... I was 'the master of this kind of thing'." The master! Gosh.

To be fair, it must have been like working in a lunatic asylum at times. It is not only that Brown's office is already at war with Blair's; there is plenty of craziness elsewhere. Campbell confirms what most of us have long suspected: that politicians (and sometimes their wives) tend to lose it once they reach high office. What to make of Blair's reading of the Bible, to be specific, of the passage in which John the Baptist denounces the marriage of Herod, who then imprisons and beheads him, shortly before the Nato bombing of Serbia? In what way did this cause him to "rethink"?

Meanwhile, Cherie is seemingly obsessed with only two things: her family's newfound poverty (25 August 1998: "CB was also complaining again that they were in real debt and it was ludicrous the things they had to spend money on without any official help") and the continued presence of Blair's foxy friend, Anji Hunter, in her husband's office (15 October 1997: "TB called… and sounded very low. He and CB had had a dreadful row last night because he had made clear Anji was staying").

Then again, perhaps the madness is contagious. Campbell's closest confidant in the battle for sanity is the football manager Alex Ferguson, the manager of Manchester United (Fergie plays the Dalai Lama to Campbell's Richard Gere). What about his wife, Fiona Millar? Alas, they are always rowing (she takes the side of Cherie in the Anji Wars), though it's hard to escape the feeling that his putative honesty about these arguments is only part of a strategy to encourage us to believe everything else.

The book is surprisingly weak on Northern Ireland; the coming and going, the endless prowling of corridors, is difficult to follow. More gripping is the section that covers the death of Diana, Princess of Wales. Campbell claims that, in the febrile days before the funeral, Prince William talked about becoming a recluse and for a while refused to countenance the idea of walking behind his mother's coffin on the grounds that it was a stunt cooked up to satisfy the hateful media. Unfortunately, William's presence beside his father was considered vital if the Prince of Wales was not to be attacked by the vengeful crowds. Can this be true? Perhaps. They were strange days.

But its inclusion here also has a whiff of revenge about it; Charles went on to brief against Blair, who much preferred the Queen. I feel similarly about the inclusion of an entry debating whether or not Peter Mandelson should come out (Campbell claims that, following the Geoffrey Robinson loan scandal, he seriously considered doing so). Mandelson has never talked about his sexuality. How is this stuff not just another tatty invasion of his privacy of the kind Campbell purports to despise?

Which brings me, neatly, to this book's raison d'être. Why publish these mammoth volumes at all? At the Hutton inquiry, Campbell said of his diary: "It is not intended for publication." Somewhere along the line, that policy changed; apparently, it would be fine to publish these books once Gordon Brown was no longer prime minister. Hmm. Forgive me if I find this line confusing. The current shadow cabinet is still crammed with people associated with New Labour. Ed Miliband was once one of Brown's closest confidants. So while it's obviously nice that Campbell is now admitting that all the things he used to deny so furiously – namely, the dysfunction at the heart of the government – were in fact true, thus confirming to voters and journalists alike that we were neither barmy nor evil, nothing he says is exactly helpful going into the future.

For my part, I'm less likely than ever to believe the things emanating from a Labour leader's office. It's not even as though Campbell offers much by way of insight or analysis. This is one-thing-after-another stuff, not proper writing; certainly, he makes no attempt to solve the great mystery of why Blair continued to facilitate Brown's progress to Number 10. For a sense of how government works, its texture and its absurdities, you're better off turning to the diaries of a mere junior minister, Chris Mullin, though I can't, in all honesty, tell you that I find any of these books terribly honourable.